The present invention relates to a system and a method for spinning up a rotary element of a mechanical device.
Although the present invention applies more specifically to the starting of a turbomachine, particularly an aircraft engine, it may be applied to any mechanical device of which a rotary mechanical element (a shaft, rotor, etc.) needs to be spun up in an environment subject to high thermomechanical stresses likely to create deformations in said rotary element.
It is known that during an airplane operating cycle, notably in the case of a short-haul or medium-haul airliner, the airplane touches down at an airport generally to unload the passengers and load other passengers before leaving for another destination. This passenger changeover generally takes between thirty minutes and one hour thirty minutes.
During this time, the airplane engines, which are switched off (for safety reasons), remain hot and do not have time to cool completely. It is estimated as a general rule that an engine is cold after having been switched off for around one hour and thirty minutes.
Thus, during the waiting time, a thermal gradient across the rotor or rotors of the engine causes certain blades and/or rotor or rotors to expand and deform (leading to a reduction in the axial or diametral clearance with respect to the normal axis of rotation of the blading, expansion of the blades, etc.).
Upon restarting, if the engine has not had time to cool sufficiently, the ends of certain rotor blades run the risk of rubbing against the casing or that some blading may be deflected from its axis of rotation a little. This phenomenon is known as a bowed rotor and lasts until the temperature across the blading becomes uniform as a result of operation (rotation and reduction of internal thermal gradients) of the engine.
This phenomenon of rotor deformation leads to an appreciable increase in fuel consumption because of a loss of aerodynamic efficiency notably of various elements of the engine, this being irreversible (because of the wearing away of the blade tips). It is therefore advantageous to be able to prevent or limit this phenomenon of rotor deformation, and this is what the present invention notably seeks to achieve.